It has heretofore been proposed to provide a cased glass stream for forming glassware having layered wall segments. U.S. application Ser. Nos. 08/374,371 and 08/374,372 disclose techniques for delivering such a cased glass stream in which core glass from a first source is delivered through a first orifice. A second orifice is vertically spaced beneath and aligned with the first orifice, and is surrounded by an annular chamber that communicates with the second orifice through the gap between the first and second orifices. A heated tube delivers casing glass from a second glass source to the annular chamber that surrounds the second orifice. Glass flows by force of gravity from the first and second sources through the first and second orifices in such a way that a cased glass stream emerges from the second orifice. This cased glass stream may be sheared by conventional techniques to form individual cased glass gobs for delivery to conventional individual section glassware forming machines.
Although the techniques disclosed in the noted patent applications address and overcome problems theretofore extant in the art, further improvements remain desirable. For example, an important factor in proper manufacture of cased glassware is maintaining a desired ratio between the casing glass and the core glass. Because of higher operating temperatures in the casing glass system, refractory erosion is high in the casing glass spout, which in turn requires that glass flow through the casing glass spout be adjusted frequently to offset erosion enlargement of the flow path. The rate of casing glass flow is also affected by changes in ambient temperature that affect drafts around the forehearth and spout, changes in the spout cover opening around the spout flow control tube, changes in the manually adjusted gas-fired heating at the spout, and jostling or disturbance at the positioning mechanism for the flow control tube. Casing glass spout flow adjustments are currently made by manually adjusting position of a flow control tube within the casing glass spout. It is a general object of the present invention to provide a method and apparatus for automatically controlling the rate of glass flow through the casing glass spout so as to maintain the desired ratio between casing and core glasses in the cased glass stream. Another and more specific object of the present invention is to provide a method and apparatus of the described character for adjusting casing glass flow in which adjustments are automatically implemented at periodic intervals for accommodating inherent delays and transient conditions in glass flow dynamics.
Apparatus for forming a cased glass stream having an inner core glass surrounded by an outer casing glass includes at least one first orifice for receiving core glass from a first source. At least one second orifice is vertically spaced beneath and aligned with the first orifice, and is surrounded by a chamber that communicates with the second orifice through a gap between the first and second orifices. A spout delivers casing glass from a second source through a tube to the chamber in such a way that glass flows by gravity from the first and second sources through the orifices to form the cased glass stream. In accordance with one aspect of the present invention, the rate of glass flow through the second or casing glass source is measured and compared with one or more preset thresholds or limits. Rate of casing glass flow from the second source to the chamber surrounding the orifices is adjusted when rate of flow through the second source departs from the desired flow rate. For example, when flow rate exceeds a desired upper limit or threshold, flow rate is automatically reduced. On the other hand, if flow rate drops below a desired lower threshold or limit, flow rate is automatically increased. In this way, the desired ratio of casing glass to core glass is automatically maintained.
In the preferred embodiment of the present invention, casing glass is delivered through a spout having a lower spout opening, and a flow control tube disposed within the spout for movement toward and away from the spout opening so as selectively to close and open the opening. The spout tube is coupled to an electric motor that is driven by electronic circuitry automatically responsive to rate of glass flow into the casing glass spout for selectively operating the motor and restricting flow through the spout opening. Movement at the casing glass flow control tube preferably is enabled only at periodic intervals so as to accommodate inherent delays associated with changes of glass flow through the system. Glass flow rate preferably is periodically measured and averaged over the measurement interval so as to accommodate transient conditions. Most preferably, the flow control tube is moved toward or away from the spout opening a predetermined distance after each measurement interval within which average glass flow rate exceeds or is below the desired flow threshold limit. This is accomplished in the preferred embodiment of the invention by use of a stepper motor, and providing to the stepper motor a predetermined number of pulses corresponding to the predetermined desired incremental travel distance at the spout tube.
In accordance with another aspect of the present invention, a method of delivering a glass stream includes the step of delivering glass from a glass batch hopper through a furnace to a spout having an opening through which the glass stream flows by force of gravity. The rate of flow of glass from the glass batch hopper through the furnace is measured, and the rate of flow from the spout opening is controlled so as to maintain the rate of flow from the glass batch hopper through the furnace within preset limits. The rate of glass flow through the spout opening is controlled by positioning a tube within the spout for movement toward and away from the opening, and controlling position of the tube with respect to the spout opening. The latter is most preferably accomplished by coupling the tube to an electric motor, and activating the motor to move the tube toward and away from the spout opening so as to maintain the rate of glass flow through the furnace within preset limits. The preferred implementation of this aspect of the invention is in a method of forming a cased glass stream wherein the rate of casing glass flow from the casing glass batch hopper through the casing glass furnace is measured, and rate of glass flow through a casing glass spout is automatically controlled so as to maintain such flow above a preset limit.